DESCRIPTION (Adapted from applicants' abstract) The long term career goal is to conduct independent research and to teach in a research-oriented university. Currently, this is the applicant's first year as an Assistant Professor of Physiology at the University of Pennsylvania. The long term goal of her research is to understand the structural and functional basis of the ability of ion channels to accomplish their biological tasks in various cell types. In this proposal, she will investigate the mechanisms of ion permeation in inward-rectifier K+ channels. These ion channels are highly selective for K+, and pass K+ in the inward direction more efficiently than in the outward direction. This latter property has been termed inward rectification. The K+ selectivity and inward rectification allow inward-rectifier K+ channels to regulate the resting membrane potential in many cells, through which they accomplish their biological tasks. The aim of the experiments proposed here is to investigate the molecular mechanisms underlying these two fundamental properties of ion permeation in inward-rectifier K+ channels. Cloned inward-rectifier K+ channels will be expressed in Xenopus oocytes and their permeation properties will be studied using electrophysiological techniques. Aim #1: To investigate the molecular determinants of the selective K+-binding site. The applicant will use a combined approach: measuring the occupancy of K+-binding sites under equilibrium conditions, and mutagenizing the channel protein. Aim #2: To investigate the mechanisms of the rectification induced by intracellular blocking ions by addressing the following questions: a. Do blocking ions inhibit outward K+ current by occupying a K+-binding site? b. Does external K+ relieve channel blockade by internal blocking ions through an electrostatic mechanism? The proposed studies have important medical implications. For example, G-protein gated inward-rectifier K+ channels mediate the regulation of heart rate by vagal nerve, and ATP-sensitive inward-rectifier K+ channels are important during cardiac ischemia. (End of Abstract)